4 fast cores or 6 slower ones?
Blender can use up to 8 cores, and it does.
For rendering, or baking the two most CPU intensive tasks, the 2.93 ghz 6 core would be better. The clock speed is not as important as computational power, and for that the more cores wins.

For Cycles a good GPU would be faster then any of those CPUs listed. However if you are rendering on the CPU (like me) then the same is true more computational power will win out over a faster clock speed.

Blender guru article on buying a computer for blender.